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We obtained cost data on 47 off-grid and 11 grid-connected systems from Home Power magazine and Solar Energy International, ranging from 100 to 6600 W installed from 1987 to 2004. This allowed accurate analysis of installed costs ($/W, corrected to 2004$) without rebates or discounts for PV modules and balance of systems (BOS)- The BOS was separated into categories of batteries, power conditioning electronics (PCE), and "other". When normalized by system size, relative off-grid BOS costs are approximately independent of system size and comparable to PV module costs, especially for systems over 1000 W. Thus the off-grid system cost is approximately twice the module cost. Off-grid BOS and PV prices have been falling at about 0.5 $/W per year since 1990. System prices have therefore been falling at ∼1 $/W per year. Grid connected systems have much lower BOS costs. Some off-grid systems with 2 axis trackers were not cost effective for maximizing the Dec-Jan output.